Method and apparatus for fabricating reformable stiffening elements

ABSTRACT

A stiffening element comprises a tension and compression member, a shear member, an attachment member, and a plurality of beads. The tension and compression member is positioned spaced apart from the skin and configured to bear tension or compression forces that stiffen the skin and prevent the skin from buckling or bending. The shear member is connected to the tension and compression member and configured to bear shear forces between the skin and the tension and compression member. The attachment member is connected to the shear member and is configured to connect to the skin. The beads each create out-of-plane feature that is positioned in at least one of the shear member and the attachment member. The beads permit the stiffening element be reshaped to adjust a longitudinal curvature of the stiffening element.

FIELD OF THE INVENTION

Embodiments of the current invention relate to components, apparatuses,and methods for fabricating reformable stiffening elements, such asaircraft stringers.

DESCRIPTION OF THE RELATED ART

A stiffening element, such as a stringer, is a structure that isattached or bonded to a skin, i.e., the outer layer, of a fuselage or awing of an aircraft, and provides structural reinforcement and preventsbuckling of the skin. Common stringer types of stiffening elementsinclude hat or omega stringers and U stringers. The omega stringer, asshown in FIG. 1, includes a cap, a pair of webs, and a pair of flanges.The cap is a planar elongated rail that is horizontally oriented in thefigure. The webs are planar elongated rails that are oriented at anoffset, diagonal angle and connected to opposing edges of the cap. Theflanges are also planar elongated rails that are horizontally orientedwith each flange being connected to a free edge of a successive one ofthe webs. The flanges, also known as the “attachment members”, provide asurface that attaches to the skin, through bolting, riveting, bonding,welding, or the like. The webs, also known as the “shear members”,provide resistance to shear forces. The cap, also known as the “tensionand compression member”, provides stiffness. The U stringer, as shown inFIG. 2, includes the same components as the omega stringer: a cap, apair of webs, and a pair of flanges. In contrast to the omega stringer,the cap of the U stringer is the attachment member and attaches to theskin, while the flanges are the tension and compression members andprovide stiffness.

A fuselage may be divided into lengthwise sections, wherein each sectionincludes a plurality of stringer type stiffening elements distributedalong a circumference of the fuselage and oriented such that alongitudinal axis of each stiffening element aligns with a longitudinalaxis of the fuselage. A portion of a fuselage with a section of the skinremoved is shown in FIG. 3 to reveal the stringers. Since the fuselagehas a curvature along its length that varies according to thelongitudinal position, the stiffening elements for each section have adifferent lengthwise shape. For example, the stiffening elementspositioned near the center of the fuselage may have a small curvature,while the stiffening elements positioned near either end of the fuselagemay have a much greater curvature.

Each stiffening element is typically formed using a die or tool that hasa curvature which matches the curvature of the fuselage for a givensection. Thus, to construct a fuselage, a plurality of custom shapedstiffening elements must be formed and a plurality of custom shaped diesare required to form them. For a typical fuselage, up to a hundredcustom shaped stiffening elements and accordingly, up to a hundredcustom shaped dies may be required. Any changes to the shape ordimensions of the fuselage, such as for a larger or smaller aircraft,requires different custom shaped dies to form different custom shapedstiffening elements. This customized approach to fuselage constructionleads to costly formation of custom shaped dies and stockpiling ofcustom shaped parts.

Another problem with prior art stiffening elements is they are typicallyvery rigid and have structural failure mechanisms that present adrawback. For example, if an incident occurred which led to a separationof just a portion of the stiffening element from the skin, thenrelatively very little energy is required to propagate the separationalong the joint of the stiffening element and the skin as a result ofthe rigidity of the stiffening element. This could lead to thestiffening element completely separating from the skin.

SUMMARY OF THE INVENTION

Embodiments of the current invention solve the above-mentioned problemsand provide a distinct advantage over prior art stringers. In oneembodiment, stiffening elements are formed from composite material andcreated to be initially straight—which means the stiffening elements areformed on a relatively inexpensive straight tool. The stiffeningelements include a plurality of longitudinally-spaced beads that allowfor each stiffening element to be reshaped in order for the stiffeningelement to acquire a longitudinal curvature that matches a curvature ofthe fuselage skin to which the stiffening element will be attached. Thecurrent invention further provides methods of reshaping the stiffeningelements, such as by reshaping the beads, that eliminate the need forcustom shaped dies or forming tools. There is also no need to stockpilecustom shaped parts for each section of the fuselage that has adifferent curvature since a stiffening element with the appropriatecurvature can be formed using the reshaping methods as needed. Inaddition, the inclusion of the beads makes the stiffening element moreflexible so that in the event of a separation of a portion of thestiffening element from the skin, the stiffening element may simply flexat one of the locations of the beads rather than continuing to separate.

A basic embodiment of the stiffening element comprises a tension andcompression member, an attachment member, a shear member extendingbetween the attachment member and the tension and compression member,and a plurality of beads formed in the attachment member and at leastpart of the shear member. The tension and compression member ispositioned spaced apart from the skin and configured to bear tension orcompression forces that stiffen the skin and prevent the skin frombuckling or bending. The shear member is connected to the tension andcompression member and configured to bear shear forces between the skinand the tension and compression member. The attachment member isconnected to the shear member and is configured to connect to the skin.The beads create out-of-plane features that are positioned, or formed,in the attachment member and at least part of the shear member. At leastone bead is configured to be reshaped to adjust a longitudinal curvatureof the stiffening element.

Another embodiment of the stiffening element comprises a tension andcompression member, first and second shear members, first and secondattachment members, and a plurality of beads. The tension andcompression member is spaced apart from the skin and is configured tobear tension or compression forces that stiffen the skin and prevent theskin from buckling or bending. The first and second shear members eachare configured to bear shear forces between the skin and the tension andcompression member. The first shear member is connected to a first sideof the tension and compression member. The second shear member isconnected to a second side of the tension and compression member. Thefirst and second attachment members are configured to connect to theskin. The first attachment member is connected to the first shear memberand the second attachment member is connected to the second shearmember. Each bead creates an out-of-plane feature that is positioned, orformed, in at least part of the shear members and in the attachmentmember. At least one bead is configured to be reshaped to adjust alongitudinal curvature of the stiffening element.

Yet another embodiment of the stiffening element comprises first andsecond tension and compression members, first and second shear members,an attachment member, and a plurality of beads. The first and secondtension and compression members are configured to bear tension orcompression forces that stiffen the skin and prevent the skin frombuckling or bending. The tension and compression members are positionedspaced apart from the skin. The first and second shear members areconfigured to bear shear forces between the skin and the first andsecond tension and compression members. The first shear member isconnected to the first tension and compression member. The second shearmember is connected to the second tension and compression member. Theattachment member is configured to connect to the skin and is connectedon one side to the first shear member and on the other side to thesecond shear member. Each bead creates an out-of-plane feature that ispositioned in the shear members and the attachment member. At least onebead is configured to be reshaped to adjust a longitudinal curvature ofthe stiffening element.

One method of reshaping a bead of a stiffening element to be attached toa skin of aircraft components comprises the steps of: attaching a clampto the bead, wherein the clamp includes an upper clamp member contactingat least a portion of a first surface of the bead, a lower clamp membercontacting at least a portion of a second, opposing surface of the bead,and a plurality of resilient members which urge the upper clamp memberto apply pressure on the stiffening element toward the lower clampmember; heating the stiffening element to a temperature above the glasstransition temperature for the stiffening element material; and reducingor removing the heat after a time period.

Another method of reshaping a bead of a stiffening element to beattached to a skin of aircraft components comprises the steps of:attaching a first clamp to the stiffening element adjacent to a firstside of the bead; attaching a second clamp to the stiffening elementadjacent to a second side of the bead; connecting a resilient memberfrom the first clamp to the second clamp; heating the stiffening elementto a temperature above the glass transition temperature for thestiffening element material; and reducing or removing the heat after atime period.

Another embodiment of the current invention provides a method ofattaching a stiffening element to a skin of aircraft components forproviding structural reinforcement comprising the steps of: placing anouter surface of the skin in contact with an upper surface of a tool;placing an attachment member of the stiffening element in contact withan inner surface of the skin; applying a force to the stiffening elementthat presses the attachment member against the skin; and attaching thestiffening element to the skin.

Yet another embodiment of the current invention provides a method ofattaching a stiffening element to a skin of aircraft components forproviding structural reinforcement comprising the steps of: placing anouter surface of the skin in contact with an upper surface of a tool;placing an attachment member of the stiffening element in contact withan inner surface of the skin; placing a vacuum bag over the stiffeningelement and the skin; sealing the vacuum bag against the upper surfaceof the tool; and applying a vacuum between the vacuum bag and the tool.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Other aspectsand advantages of the current invention will be apparent from thefollowing detailed description of the embodiments and the accompanyingdrawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the current invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a perspective view of a first type of prior art stiffeningelement;

FIG. 2 is a perspective view of a second type of prior art stiffeningelement;

FIG. 3 is a perspective view of a portion of a fuselage with a sectionof aircraft skin removed;

FIG. 4 is a perspective view of a stiffening element, constructed inaccordance with various embodiments of the current invention, thestiffening element including a tension and compression member, first andsecond shear members, an attachment member, and a plurality of beads;

FIG. 5 is a side view of the stiffening element;

FIG. 6 is a perspective view of a stiffening element including a tensionand compression member, first and second shear members, an attachmentmember, and a plurality of beads;

FIG. 7 is a side view of the stiffening element;

FIG. 8 is a perspective view of a stiffening element, constructed inaccordance with other embodiments of the current invention, thestiffening element including a tension and compression member, a shearmember, an attachment member, and a plurality of beads;

FIG. 9 is a perspective view of the stiffening element of FIGS. 4 and 5formed by joining two of the stiffening elements of FIG. 8;

FIG. 10 is a perspective view of the stiffening element of FIGS. 6 and 7formed by joining two of the stiffening elements of FIG. 8;

FIG. 11 is a perspective view of a stiffening element, constructed inaccordance with other embodiments of the current invention, thestiffening element including a tension and compression member, a shearmember, an attachment member, and a plurality of beads;

FIG. 12 is a perspective view of an “I-beam” formed by joining two ofthe stiffening elements of FIG. 11;

FIG. 13 is a listing of at least a portion of the steps of a firstmethod of reshaping a bead of a stiffening element;

FIG. 14 is an upper perspective exploded view of a first clampconfigured to flatten a bead of the stiffening element;

FIG. 15 is a lower perspective exploded view of the first clamp;

FIG. 16 is an upper perspective exploded view of a second clampconfigured to enhance a bead of the stiffening element;

FIG. 17 is a lower perspective exploded view of the second clamp;

FIG. 18 is an upper perspective exploded view of a first clampconfigured to flatten a bead of the stiffening element;

FIG. 19 is a lower perspective exploded view of the first clamp;

FIG. 20 is an upper perspective exploded view of a second clampconfigured to enhance a bead of the stiffening element;

FIG. 21 is a lower perspective exploded view of the second clamp;

FIG. 22 is an upper perspective view of the stiffening element with thefirst clamp attached to flatten a first bead and the second clampattached to enhance a second bead;

FIG. 23 is a lower perspective view of the stiffening element with thefirst clamp and the second clamp;

FIG. 24 is a top view of the stiffening element with the first clamp andthe second clamp;

FIG. 25 is a side view of the stiffening element with the first clampand the second clamp;

FIG. 26 is a side sectional view of the stiffening element with thefirst clamp and the second clamp cut along the line 21-21 in FIG. 19;

FIG. 27 is an upper perspective view of the stiffening element with thefirst clamp and the second clamp after heat has been applied to thestiffening element and the first and second beads have been reshaped;

FIG. 28 is a side view of the stiffening element with the first clampand the second clamp after heat has been applied to the stiffeningelement and the first and second beads have been reshaped;

FIG. 29 is a side sectional view of the stiffening element with thefirst clamp and the second clamp after heat has been applied to thestiffening element and the first and second beads have been reshaped;

FIG. 30 is an upper perspective view of the stiffening element afterheat has been applied and the clamps have been removed;

FIG. 31 is a lower perspective view of the stiffening element after heathas been applied and the clamps have been removed;

FIG. 32 is a side view of the stiffening element after heat has beenapplied and the clamps have been removed;

FIG. 33 is an upper perspective view of the stiffening element with thefirst clamp attached to flatten a first bead and the second clampattached to enhance a second bead;

FIG. 34 is a lower perspective view of the stiffening element with thefirst clamp and the second clamp;

FIG. 35 is a bottom view of the stiffening element with the first clampand the second clamp;

FIG. 36 is a side view of the stiffening element with the first clampand the second clamp;

FIG. 37 is a side sectional view of the stiffening element with thefirst clamp and the second clamp cut along the line 32-32 in FIG. 30;

FIG. 38 is an upper perspective view of the stiffening element with thefirst clamp and the second clamp after heat has been applied to thestiffening element and the first and second beads have been reshaped;

FIG. 39 is a side view of the stiffening element with the first clampand the second clamp after heat has been applied to the stiffeningelement and the first and second beads have been reshaped;

FIG. 40 is a side sectional view of the stiffening element with thefirst clamp and the second clamp after heat has been applied to thestiffening element and the first and second beads have been reshaped;

FIG. 41 is an upper perspective view of the stiffening element afterheat has been applied and the clamps have been removed;

FIG. 42 is a lower perspective view of the stiffening element after heathas been applied and the clamps have been removed;

FIG. 43 is a side view of the stiffening element after heat has beenapplied and the clamps have been removed;

FIG. 44 is a listing of at least a portion of the steps of a secondmethod of reshaping a bead of a stiffening element;

FIG. 45 is an upper perspective exploded view of a clamp that is acomponent of a first clamp assembly configured to reshape a bead of thestiffening element;

FIG. 46 is an upper perspective view of the clamp of FIG. 40;

FIG. 47 is an upper perspective exploded view of a clamp that is acomponent of a first clamp assembly configured to reshape a bead of thestiffening element;

FIG. 48 is a lower perspective exploded view of the clamp of FIG. 42;

FIG. 49 is an upper perspective view of a clamp that is a component of asecond clamp assembly configured to reshape a bead of the stiffeningelement;

FIG. 50 is an upper perspective view of the first clamp assemblyattached to the stiffening element and configured to flatten a bead;

FIG. 51 is an upper perspective view of the stiffening element afterheat has been applied and the bead has been flattened;

FIG. 52 is a side view of the stiffening element after heat has beenapplied and the bead has been flattened;

FIG. 53 is an upper perspective view of a second clamp assembly attachedto the stiffening element and configured to enhance a bead;

FIG. 54 is an upper perspective view of the stiffening element afterheat has been applied and the bead has been enhanced;

FIG. 55 is a side view of the stiffening element after heat has beenapplied and the bead has been enhanced;

FIG. 56 is an upper perspective view of the first clamp assemblyattached to the stiffening element and configured to enhance a bead;

FIG. 57 is a side sectional view of the first clamp assembly attached tothe stiffening element;

FIG. 58 is an upper perspective view of the stiffening element afterheat has been applied and the bead has been enhanced;

FIG. 59 is a side sectional view of the stiffening element after heathas been applied and the bead has been enhanced;

FIG. 60 is an upper perspective view of the second clamp assemblyattached to the stiffening element and configured to flatten a bead;

FIG. 61 is an upper perspective view of the stiffening element afterheat has been applied and the bead has been enhanced;

FIG. 62 is a listing of at least a portion of the steps of a firstmethod of attaching a stiffening element to a skin;

FIG. 63 is an upper perspective view of the stiffening element placed onthe skin which is placed on an upper surface of a tool;

FIG. 64 is a side view of the stiffening element receiving a force orpressure applied to attach the stiffening element to the skin;

FIG. 65 is an upper perspective view of the stiffening element after ithas been attached to the skin and a plurality of beads have been atleast partially flattened;

FIG. 66 is a side view of the stiffening element after it has beenattached to the skin and a plurality of beads have been at leastpartially flattened;

FIG. 67 is a listing of at least a portion of the steps of a secondmethod of attaching a stiffening element to a skin;

FIG. 68 is an upper perspective view of the stiffening element placed onthe skin which is placed on an upper surface of a tool, all of which isto be covered by a vacuum bag;

FIG. 69 is a side view of the stiffening element receiving a force orpressure applied from the vacuum bag to attach the stiffening element tothe skin; and

FIG. 70 is a side view of the stiffening element after it has beenattached to the skin and a plurality of beads have been at leastpartially flattened.

The drawing figures do not limit the current invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description of the technology references theaccompanying drawings that illustrate specific embodiments in which thetechnology can be practiced. The embodiments are intended to describeaspects of the technology in sufficient detail to enable those skilledin the art to practice the technology. Other embodiments can be utilizedand changes can be made without departing from the scope of the currentinvention. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the current invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

A stiffening element 10, constructed in accordance with variousembodiments of the current invention, for providing structuralreinforcement for a skin 12, or similar component, of an aircraft isshown in FIGS. 4 and 5. Typically, the skin 12 is an outer component orlayer of an aircraft fuselage, as shown in FIG. 3. The stiffeningelement 10 may be similar to the hat or omega stringer. The stiffeningelement 10 broadly comprises a tension and compression member 14, firstand second shear members 16A, 16B, first and second attachment members18A, 18B, and a plurality of beads 20, which may be provided in eachattachment member 18A, 18B, and partly in each shear member 16A, 16B.

The tension and compression member 14 is a generally planar elongatedflange, beam, rail, or plank that provides stiffness and structuralstrength. The tension and compression member 14 bears, or carries,compression or tension forces acting on the skin 12 and/or resultingfrom bending of the skin 12 thereby stiffening the skin 12 andpreventing it from buckling. The tension and compression member 14 isspaced apart from, positioned offset from, or positioned away from, theskin 12, such that it is typically inward from the skin 12.

The first and second shear members 16A, 16B each may be a generallyplanar web extending between each of the first and second attachmentmembers, respectively, and opposite sides of the tension and compressionmember 14. The shear members 16A, 16B bear, or carry, the shear forcesbetween the tension and compression member 14 and the skin 12. Eachshear member 16A, 16B is preferably oriented at a generally diagonalangle away from the tension and compression member 14. For example, ifthe tension and compression member 14 is positioned on a horizontalplane, then the first side edge of the first shear member 16A may beconnected to a first side edge of the tension and compression member 14at an angle in the range of approximately 30 degrees to approximately 90degrees. An exemplary connection angle may be approximately 60 degrees.The first side edge of the second shear member 16B may be connected to asecond side edge of the tension and compression member 14 at an angle inthe range of approximately 90 degrees to approximately 150 degrees. Anexemplary connection angle may be approximately 120 degrees. Restated inanother way, the included angle between the first shear member 16A andthe second shear member 16B may be in the range of approximately 0degrees to approximately 120 degrees. An exemplary included anglebetween the first shear member 16A and the second shear member 16B maybe approximately 60 degrees. In various embodiments, the connection,joint, or intersection of the first and second shear members 16A, 16Bwith the tension and compression member 14 may be filleted, rounded,arcuate, or may have another curvature.

In various embodiments, the connection, joint, or intersection of thefirst and second attachment members 18A, 18B with their respective shearmembers 16A, 16B may be filleted, rounded, arcuate, or may have anothercurvature. In most embodiments, the attachment members 18A, 18B roughlyalign (may be generally parallel) with one another and are roughlyparallel to the tension and compression member 14. The attachmentmembers 18A, 18B are configured to attach to the skin 12.

In general, the attachment members 18A, 18B couple the skin 12 to thetension and compression member 14 through the shear members 16A, 16Bsuch that any bending of the skin 12 also necessarily stretches orcompresses the tension and compression member 14.

Each bead 20 may be an undulation, ripple, or wave that creates anout-of-plane feature that may be positioned (e.g., formed) in each ofthe attachment members 18A, 18B, and can extend at least partially intothe shear members 16A, 16B. Each bead 20 may have an arch or roughlyparabolic cross-sectional shape. Each bead 20 is illustrated having thesame cross-sectional shape, but different beads 20 could have differentcross sectional shapes. Each bead 20 extends transversely from the freeedge of each of the attachment members 18A, 18B, across each attachmentmembers 18A, 18B, and further extends into at least a portion ofrespective first and second shear members 16A, 16B. The beads 20 areformed protruding outwardly from (e.g., from the outside surface of) theomega-shaped stiffening member 10. Each bead 20 may be configured to bereshaped to adjust a longitudinal curvature of the stiffening element10. Alternatively, some of the beads 20 may not be configured to bereshaped, in which case adjustment of the longitudinal curvature of thestiffening element 10 may be accomplished by reshaping certain beads 20selected from those which are configured to be reshaped.

The stiffening element 10 may have a height of approximately 1.2 inchesand a total width of approximately 4.6 inches. The tension andcompression member 14 may have a width of approximately 1 inch. Eachshear member 16A, 16B may have a width of approximately 1.2 inches. Eachattachment member 18A, 18B may have a width of approximately 0.9 inches.Each bead 20 may have a width at the edge of the attachment members 18A,18B (i.e., a maximum width) of approximately 0.4 inches and a height (ordepth) of approximately 0.2 inches, but different beads 20 can havedifferent dimensions. The spacing from a center of one bead 20 to acenter of an adjacent bead 20 may be approximately 2 inches, but thisdimension may also vary between different adjacent beads 20. In somesituations, the skin 12, or other component to which the stiffeningelement 10 attaches, may include features on the attachment surface thatstick up, or rise, from the generally planar surface (e.g., ply ramps ordoubler locations). These features may have spacing or other relevantdimensions that are known. Accordingly, in some embodiments of thestiffening element 10, the spacing from a center of one bead 20 to acenter of an adjacent bead 20 may match (or may be selected to becompatible with) the spacing, or other dimensions, of the skin 12features.

The stiffening element 10 may be formed from thermoplastic compositematerials which broadly include a reinforcement fiber and a matrixresin. Primary types of reinforcement fiber include carbon fiber andglass fiber, while matrix resins include polyphenylene sulfide (PPS),polyetheretherketone (PEEK), polyarylether ketone (PAEK),polyetherketoneketone (PEKK), polyetherimide (PEI), and so forth. Thestiffening element 10 may be formed using continuous compression molding(CCM) or other manufacturing techniques. In various embodiments, thestiffening element 10 may be formed as a monolithic unit.

A stiffening element 30, constructed in accordance with otherembodiments of the current invention, is shown in FIGS. 6 and 7. Thestiffening element 30 also provides structural reinforcement and may beutilized interchangeably with the stiffening element 10. The stiffeningelement 30 may be similar to the U stringer. The stiffening element 30broadly comprises an attachment member 32, first and second shearmembers 34A, 34B, first and second tension and compression members 36A,36B, and a plurality of beads 38 formed in the attachment member 32 andat least part of the first and second shear members 34A, 34B.

In this embodiment, the attachment member 32 is a single generallyplanar elongated flange, beam, rail, or plank which is configured toattach to the skin 12 (as compared to the pair of attachment members18A, 18B of the embodiment illustrated in FIGS. 4-5).

The first and second shear members 34A, 34B each may be a generallyplanar elongated flange, beam, rail, or plank extending from one of theopposing sides of the attachment member 32. The shear members 34A, 34Bbear, or carry, the shear forces between the compression and tensionmembers 36A, 36B and the skin 12. Each shear member 34A, 34B may beoriented at a generally right angle, or approximately 90 degrees, withrespect to the attachment member 32. In various embodiments, theconnection, joint, or intersection of the first and second shear members34A, 34B with the attachment member 32 may be filleted, rounded,arcuate, or may have another curvature.

The tension and compression member in this embodiment is a pair oftension and compression members 36A, 36B (as compared to the singletension and compression member 14 of the embodiment illustrated in FIGS.4-5). The tension and compression members 36A, 36B bear, or carry,compression or tension forces that stiffen the skin 12 and prevent theskin 12 from bending or buckling. The tension and compression members36A, 36B are spaced apart from, positioned offset from, or positionedaway from, the skin 12, such that they are typically inward from theskin 12. The tension and compression members 36A, 36B can each be agenerally planar elongated flange, beam, rail, or plank. A side edge ofthe first tension and compression member 36A is connected to the secondside edge of the first shear member 34A, while a side edge of the secondtension and compression member 36B is connected to the second side edgeof the second shear member 34B. The first tension and compression member36A is oriented at a generally right angle, or approximately 90 degrees,with respect to the first shear member 34A. The second tension andcompression member 36B is oriented at a generally right angle, orapproximately 90 degrees, with respect to the second shear member 34B.In various embodiments, the connection, joint, or intersection of thefirst and second tension and compression members 36A, 36B with theirrespective shear members 34A, 34B may be filleted, rounded, arcuate, ormay have another curvature. In most embodiments, the first and secondtension and compression members 36A, 36B roughly align with one anotherand are roughly parallel to the attachment member 32. The tension andcompression members 36A, 36B provide stiffness and structural strength.The tension and compression members 36A, 36B bear, or carry, compressionor tension forces that act on the skin 12 and/or result from bending ofthe skin 12.

In general, the attachment member 32 couples the skin 12 to the tensionand compression members 36A, 36B through the shear members 34A, 34B suchthat any bending of the skin 12 also necessarily stretches or compressesthe tension and compression members 36A, 36B.

Each bead 38 may be an undulation, a ripple, or a wave that creates anout-of-plane feature that is positioned, or formed, in the attachmentmember 32 and at least part of the shear members 34A, 34B. Each bead 38may have an arch or roughly parabolic cross-sectional shape. Each bead38 is illustrated having the same cross-sectional shape, but differentbeads 38 may have different cross sectional shapes. Each bead 38preferably has the same cross-sectional shape, but different beads 38could have different cross sectional shapes. Each bead 38 extendstransversely across the attachment member 32, and further extends intoat least a portion of respective first and second shear members 34A,34B. The beads 38 in this embodiment are formed protruding inwardly from(e.g., from the inside surface of) the U-shaped stiffening member 30.The beads 38 are spaced apart from one another along the lengths of thefirst and second shear members 34A, 34B and the attachment member 32.Each bead 38 may be configured to be reshaped to adjust a longitudinalcurvature of the stiffening element 30. Alternatively, some of the beads38 may not be configured to be reshaped, in which case adjustment of thelongitudinal curvature of the stiffening element 30 may be accomplishedby reshaping certain beads 38 selected from those which are configuredto be reshaped.

The stiffening element 30 may have a height of approximately 1.25 inchesand a total width of approximately 2.4 inches. The attachment member 32may have a width of approximately 1.2 inches. Each shear member 34A, 34Bmay have a width of approximately 1.2 inches. Each of the first andsecond tension and compression members 36A, 36B may have a width ofapproximately 0.6 inches. Each bead 38 may have a maximum width ofapproximately 0.4 inches and a depth of approximately 0.2 inches, butdifferent beads 38 may have different dimensions. The spacing from acenter of one bead 38 to a center of an adjacent bead 38 isapproximately 2 inches, but this dimension may also vary betweendifferent adjacent beads 38. Like the stiffening element 10, thestiffening element 30 may be utilized with a skin 12 that includesattachment surface features. And accordingly, in some embodiments of thestiffening element 30, the spacing from a center of one bead 38 to acenter of an adjacent bead 38 may match (or may be selected to becompatible with) the spacing, or other dimensions, of the skin 12features.

Like the stiffening element 10, the stiffening element 30 may be formedfrom thermoplastic composite materials and may be formed as a monolithicunit.

A stiffening element 40, constructed in accordance with otherembodiments of the current invention, is shown in FIG. 8. The stiffeningelement 40 also provides structural reinforcement and may be considered,or similar to, a “Z” stringer. The stiffening element 40 broadlycomprises a tension and compression member 42, a shear member 44, anattachment member 46, and a plurality of beads 48.

The tension and compression member 42 includes a generally planarelongated flange, beam, rail, or plank that provides stiffness andstructural strength. The tension and compression member 42 bears, orcarries, compression or tension forces that stiffen the skin 12 andprevent the skin 12 from bending or buckling. The tension andcompression member 42 is spaced apart from, positioned offset from, orpositioned away from, the skin 12, such that it is typically inward fromthe skin 12.

The shear member 44 may be a generally planar elongated flange, beam,rail, or plank with a first side edge connected to the tension andcompression member 42. The shear member 44 may bear, or carry, the shearforces between the tension and compression member 42 and the skin 12.The shear member 44 may be oriented at a nonzero angle with respect tothe tension and compression member 42. For example, if the tension andcompression member 42 is positioned on a horizontal plane, then thefirst side edge of the shear member 44 may be connected to a first sideedge of the tension and compression member 42 at an angle in the rangeof approximately 60 degrees to approximately 120 degrees. In variousembodiments, the connection, joint, or intersection of the shear member44 with the tension and compression member 42 may be filleted, rounded,arcuate, or may have another curvature.

The attachment member 46 may be a generally planar elongated flange,beam, rail, or plank. The attachment member 46 is connected to the shearmember 44. In various embodiments, the connection, joint, orintersection of the attachment member 46 with the shear member 44 may befilleted, rounded, arcuate, or may have another curvature. In thisZ-shaped configuration, the attachment member 46 and the tension andcompression member 42 each extend away from the shear member 44 inopposing directions. The attachment member 46 is configured to attach tothe skin 12.

In general, the attachment member 46 couples the skin 12 to the tensionand compression member 42 through the shear member 44 such that anybending of the skin 12 also necessarily stretches or compresses thetension and compression member 42.

Each bead 48 may be an undulation, a ripple, or a wave creating anout-of-plane feature that is, as in previously described embodiments,positioned partially in the shear member 44 and may extend acrosssubstantially the entire width of the attachment member 46. The bead 48may have an arch or roughly parabolic cross-sectional shape. The bead 48extends in a transverse direction across the attachment member 46 andtransversely into and across at least part of the shear member 44. Thebeads 48 are spaced apart from one another along the length of thestiffening element 40. The beads 48 may have the same dimensions andspacing along the stiffening element 40, or their dimensions and spacingmy vary. Some, all, or only a portion of the beads 48 may be configuredto be reshaped, in the same way as described above in connection withthe embodiments illustrated in FIGS. 4-7.

The stiffening element 40 may be utilized as a component to form eitherthe stiffening element 10 or the stiffening element 30. When forming thestiffening element 10, two stiffening elements 40 are joined along thefree edge of the tension and compression member 42 as shown in FIG. 9.When forming the stiffening element 30, two stiffening elements 40 arejoined along the free edge of the attachment member 46 as shown in FIG.10.

A stiffening element 50, constructed in accordance with otherembodiments of the current invention, is shown in FIG. 11. Thestiffening element 50 also provides structural reinforcement and may beconsidered, or similar to, a “C” stringer. The stiffening element 50broadly comprises a tension and compression member 52, a shear member54, an attachment member 56, and a plurality of beads 58.

The tension and compression member 52 includes a generally planarelongated flange, beam, rail, or plank that provides stiffness andstructural strength. The tension and compression member 52 bears, orcarries, compression or tension forces that stiffen the skin 12 andprevent the skin 12 from bending or buckling. The tension andcompression member 52 is spaced apart from, positioned offset from, orpositioned away from, the skin 12, such that it is typically inward fromthe skin 12.

The shear member 54 may be a generally planar web with a first edgeconnected to the tension and compression member 52 and an opposite edgeconnected to the attachment member 56. The shear member 54 can bear, orcarry, the shear forces between the tension and compression member 52and the skin 12. The shear member 54 may be oriented at a nonzero anglewith respect to the tension and compression member 52. For example, ifthe tension and compression member 52 is positioned on a horizontalplane, then edge of the shear member 54 may be connected to the edge ofthe tension and compression member 52 at an angle in the range ofapproximately 60 degrees to approximately 120 degrees. In variousembodiments, the connection, joint, or intersection of the shear member54 with the tension and compression member 52 may be filleted, rounded,arcuate, or may have a curvature.

The attachment member 56 can be a generally planar elongated flange,beam, rail, or plank. The attachment member 56 is connected to one edgeof the shear member 54 opposite the edge of the shear member 54 that isconnected to the tension and compression member 52. In variousembodiments, the connection, joint, or intersection of the attachmentmember 56 with the shear member 54 may be filleted, rounded, arcuate, ormay have another curvature. In this C-shaped configuration theattachment member 56 and the tension and compression member 52 eachextend away from the shear member 54 in the same direction. Theattachment member 56 is configured to attach to the skin 12.

In general, the attachment member 56 couples the skin 12 to the tensionand compression member 52 through the shear member 54 such that anybending of the skin 12 also necessarily stretches or compresses thetension and compression member 52.

Each bead 58 includes an undulation, a ripple, or a wave creating anout-of-plane feature that is positioned in the shear member 54 and theattachment member 56. The bead 58 may have an arch or roughly paraboliccross-sectional shape. The bead 58 is formed at least partly in theshear member 54 and extends in a transverse direction across the shearmember 54 and extends into and across the entire width of the attachmentmember 56. The beads 58 are spaced apart from one another along thelength of the stiffening element 50. The beads 50 may have the samedimensions, and spacing along the stiffening element 40, or theirdimensions and spacing my vary. All, some, or only a portion of thebeads 48 may be configured to be reshaped, as described above inconnection with the embodiments illustrated in FIGS. 4-7.

The stiffening element 50 may be utilized as a component to form an“I-beam” whose curvature along a longitudinal axis may be adjusted. Toform the I-beam as shown in FIG. 12, two stiffening elements 50 may bejoined, e.g., using fasteners or adhesive, along the shear member 54,such that the shear members 54 are joined with one another.Alternatively or additionally, the tension and compression members 52 ofthe two stiffening elements 50 may be joined by adding additionalelongated flange, beam, rail, or plank (not shown) that spans acrossboth tension and compression members 52 and attaches to each. Suchadditional elongated flange, beam, rail, or plank may be a ply ofcomposite material.

Although the terms “tension and compression member” and “shear member”are sometimes described herein as including or comprising a “generallyplanar elongated flange, beam, rail, or plank,” one having ordinaryskill in the art will readily understand that these are generalizationsof typical stiffener configurations and should not be interpreted aslimiting. In particular, the present invention may also be applied tobulb stiffeners and stiffeners having sinusoidal webs such as thestiffeners disclosed in co-pending U.S. patent application Ser. No.16/690,445 (the “'445 application”), which is hereby incorporated hereinby reference in its entirety. For example, the web 26 of the bulbstiffener 22 shown in FIG. 6 of the '445 application should beunderstood to be a “shear member” although it is not completely planar.Likewise, the bulb cap 24 of the bulb stiffener 22 shown in FIG. 6 ofthe '445 application should be understood to be a “tension andcompression member” although it is not generally planar and does nothave a constant thickness as the terms flange or plank may suggest. Invarious embodiments of the present invention, the tension andcompression member may be a bulb member and/or the shear member may be asine wave web.

It should also be understood that the use of the phrase “connected to”herein to describe the physical relationship between the variousfeatures of the stiffening element should not be construed to imply thatthe invention must be practiced by literally connecting discrete piecesin an assembly operation to form a completed stiffening element. Indeed,it is contemplated by the inventor that stiffening elements made inaccordance with the present invention will most often be formed asmonolithic units.

A listing of at least a portion of the steps of a first method 1000 ofreforming or reshaping a stiffening element, such as the stiffeningelements 10, 30, is shown in FIG. 13. The steps may be performed in theorder shown in FIG. 13, or they may be performed in a different order.Furthermore, some steps may be performed concurrently as opposed tosequentially. In addition, some steps may be optional or may not beperformed. The reforming or shaping of the stiffening element 10, 30 isperformed to provide a longitudinal or lengthwise curvature to thestiffening element 10, 30 such that its longitudinal curvature roughlymatches that of the inner surface of the skin 12 to which the stiffeningelement 10, 30 is to be attached. Typically, the skin 12 has a convexcurvature. But, in some cases, the skin 12, or features or componentsattached to the inner surface of the skin 12, may have a concavecurvature.

The reforming of the stiffening elements 10, 30 (to change theirlongitudinal curvature) is accomplished by applying forces to the beads20, 38 as necessary to reshape the beads 20, 38. The nature of the forceapplied determines the new shape that the bead 20, 38 will have. Forexample, applying a force or pressure to the exterior of the bead 20flattens, or decreases the height or depth of, the bead 20, 38, whileapplying a force or pressure to the interior of the bead 20 enhances, orincreases the height or depth of, the bead 20, 38. Flattening the bead20, 38 results in a convex curvature of the stiffening element 10, 30,and enhancing the bead 20, 38 results in a concave curvature of thestiffening element 10, 30.

The method 1000 utilizes clamps to reshape the beads 20, 38. The clampvaries according to whether the bead 20, 38 is on the stiffening element10 or the stiffening element 30 and whether the bead 20, 38 is to beflattened or enhanced. Thus, there are four types of clamps. There is afirst clamp 100 for flattening the bead 20 of the stiffening element 10,a second clamp 102 for enhancing the bead 20, a third clamp 104 forflattening the bead 38 of the stiffening element 30, and a fourth clamp106 for enhancing the bead 38.

Referring to FIGS. 14 and 15, the first clamp 100 (for flattening thebead 20) includes an upper clamp member 108, a lower clamp member 110,and first and second fasteners 112, 114. The upper clamp member 108includes first and second vertical walls 116, 118, a horizontal wall120, and first and second bolt walls 122, 124. Each wall may have agenerally rectangular box shape. The first and second vertical walls116, 118 are spaced apart from one another, with the horizontal wall 120positioned therebetween, connected to an upper edge of each verticalwall 116, 118. The first and second bolt walls 122, 124 each include athrough hole to receive a fastener such as a bolt. The first bolt wall122 is connected to an outer surface of the first vertical wall 116,while the second bolt wall 124 is connected to an outer surface of thesecond vertical wall 118. Each of the vertical walls 116, 118 includes aconcave face to contact at least a portion of the bead 20, wherein theconcave face has a recess, an indentation, or a depression that has adepth smaller than a height of the bead 20 to be flattened.

The lower clamp member 110 includes first and second vertical walls 126,128, a horizontal wall 130, and first and second bolt walls 132, 134.Each wall may have a generally rectangular box shape. The first andsecond vertical walls 126, 128 are spaced apart from one another, withthe horizontal wall 130 positioned therebetween, connected to a loweredge of each vertical wall 126, 128. The first and second bolt walls132, 134 each include a through hole to receive a fastener such as abolt. The first bolt wall 132 is connected to an outer surface of thefirst vertical wall 126, while the second bolt wall 134 is connected toan outer surface of the second vertical wall 128. Each of the verticalwalls 126, 128 includes a convex face to contact at least a portion ofthe bead 20, wherein the convex face has a ridge, a bulge, or aprotrusion that has a height smaller than a depth of the bead 20 to beflattened. The first and second vertical walls 126, 128 generally alignwith the first and second vertical walls 116, 118. And, the convex facesof the first and second vertical walls 126, 128 are generallycomplementary to the concave faces of the first and second verticalwalls 116, 118.

The first and second fasteners 112, 114 each include a bolt, a nut, anda spring. For each fastener 112, 114, the spring is placed coaxially onthe bolt. Each bolt is placed through the holes in the bolt walls 122,124, 132, 134 so that the spring rests on the upper surface of the firstand second bolt walls 122, 124. Each nut is attached to one of the boltsin a traditional manner.

Referring to FIGS. 16 and 17, the second clamp 102 (for enhancing thebead 20) includes an upper clamp member 136, a lower clamp member 138,and first and second fasteners 140, 142. The upper clamp member 136includes first and second vertical walls 144, 146, a horizontal wall148, and first and second bolt walls 150, 152. The lower clamp member138 includes first and second vertical walls 154, 156, a horizontal wall158, and first and second bolt walls 160, 162. The first and secondfasteners 140, 142 each include a bolt, a nut, and a spring. The secondclamp 102 is substantially similar to the first clamp 100, except thateach concave face of the vertical walls 144, 146 has a recess, anindentation, or a depression that receives the bead 20 to be enhanced.And, each convex face of the vertical walls 154, 156 has a ridge, abulge, or a protrusion that has a height greater than the bead 20 to beenhanced.

Referring to FIGS. 18 and 19, the third clamp 104 (for flattening thebead 38) includes an upper clamp member 164, a lower clamp member 166,and first and second fasteners 168, 170. The upper clamp member 164includes first and second bolt walls 172, 174 and an upper central wall176. Each wall may have a generally rectangular box shape. The first andsecond bolt walls 172, 174 each include a through hole to receive afastener such as a bolt. The first and second bolt walls 172, 174 areconnected to one another to form an elongated beam. The upper centralwall 176 is connected to the intersection of the first and second boltwalls 172, 174. The upper central wall 176 includes a convex face tocontact at least a portion of the bead 38, wherein the convex face has aridge, a bulge, or a protrusion that has a height smaller than a depthof the bead 38 to be flattened.

The lower clamp member 166 includes first and second bolt walls 178, 180and a lower central wall 182. Each wall may have a generally rectangularbox shape. The first and second bolt walls 178, 180 each include athrough hole to receive a fastener such as a bolt. The first and secondbolt walls 178, 180 are connected to one another to form an elongatedbeam. The lower central wall 182 is connected to the intersection of thefirst and second bolt walls 178, 180. The lower central wall 182includes a concave face to contact at least a portion of the bead 38,wherein the concave face has a recess, an indentation, or a depressionthat has a depth smaller than a height of the bead 38 to be flattened.The lower central wall 182 generally aligns with the upper central wall176. And, the concave face of the lower central wall 182 is generallycomplementary to the convex face of the upper central wall 176.

The first and second fasteners 168, 170 each include a bolt, a nut, anda spring. For each fastener 168, 170, the spring is placed coaxially onthe bolt. Each bolt is placed through the holes in the bolt walls 172,174, 178, 180 so that the spring rests on the upper surface of the firstand second bolt wall 172, 174. Each nut is attached to one of the boltsin a traditional manner.

Referring to FIGS. 20 and 21, the fourth clamp 106 (for enhancing thebead 38) includes an upper clamp member 184, a lower clamp member 186,and first and second fasteners 188, 190. The upper clamp member 184includes first and second bolt walls 192, 194 and an upper central wall196. The lower clamp member 186 includes first and second bolt walls198, 200 and a lower central wall 202. The first and second fasteners188, 190 each include a bolt, a nut, and a spring. The fourth clamp 106is substantially similar to the third clamp 104, except that the convexface of the upper central wall 196 has a ridge, a bulge, or a protrusionthat has a height greater than the bead 38 to be enhanced. And, theconcave face of the lower central wall 202 has a recess, an indentation,or a depression that receives the bead 38 to be enhanced.

Referring to step 1001, one of the four types of clamps 100, 102, 104,106 is attached to each bead 20, 38 that is desired to be reshaped. Forflattening a bead 20, the first clamp 100 is utilized. For enhancing abead 20, the second clamp 102 is utilized. For flattening a bead 38, thethird clamp 104 is utilized. For enhancing a bead 38, the fourth clamp106 is utilized.

Generally, one of the lower clamp members 110, 138, 166, 186 is placedon a work surface. The stiffening element 10, 30 is placed on the lowerclamp member 110, 138, 166, 186. And, a corresponding one of the upperclamp members 108, 136, 164, 184 is placed on the stiffening element 10,30. The one of the lower clamp members 110, 138, 166, 186 contacts atleast a portion of a first surface of the bead 20, 38, and thecorresponding one of the upper clamp members 108, 136, 164, 184 contactsat least a portion of a second, opposing surface of the bead 20, 38.FIGS. 22-29 illustrate the stiffening element 10 with the first clamp100 being utilized to flatten a first bead 20 and the second clamp 102being utilized to enhance a second bead 20. During attachment, theridges and the recesses of the first and second vertical walls 116, 118,126, 128, 144, 146, 154, 156 are aligned with the bead 20, and theconvex and concave faces of the first and second vertical walls 116,118, 126, 128, 144, 146, 154, 156 contact the attachment member 18.FIGS. 33-40 illustrate the stiffening element 30 with the third clamp104 being utilized to flatten a first bead 38 and the fourth clamp 106being utilized to enhance a second bead 38. During attachment, theridges and the recesses of the upper and lower central walls 176, 182,196, 202 are aligned with the bead 38, and the convex and concave facesof the upper and lower central walls 176, 182, 196, 202 contact theattachment member 32. After placement of the clamps 100, 102, 104, 106on the stiffening elements 10, 30, the bolts of each fastener 112, 114,140, 142, 168, 170, 188, 190 are placed through the respective holes ofthe bolt walls 122, 124, 132, 134, 150, 152, 160, 162, 172, 174, 178,180, 192, 194, 198, 200 and the nuts are attached and tightened.

While the stiffening element 10, 30 is in the clamp 100, 102, 104, 106as the nuts are tightened on the bolts, the springs of the fasteners112, 114, 140, 142, 168, 170, 188, 190 apply a downward force orpressure on the upper clamp member 108, 136, 164, 184, which in turnapplies a force or pressure on the stiffening element 10, 30 toward thelower clamp member 110, 138, 166, 186.

Referring to step 1002, the stiffening element 10, 30 is heated to atemperature above the glass transition temperature for the material ofthe stiffening element 10, 30. At this temperature, the stiffeningelement 10, 30 becomes malleable and the forces or pressures applied bythe springs of the fasteners 112, 114, 140, 142, 168, 170, 188, 190 urgethe convex and concave faces to reshape the bead 20, 38. If the firstclamp 100 or the third clamp 104 was utilized, then the bead 20, 38 isflattened. If the second clamp 102 or the fourth clamp 106 was utilized,then the bead 20, 38 is enhanced.

Referring to step 1003, after a time period, the heat is reduced orremoved and the stiffening element 10, 30 is removed from the clamp 100,102, 104, 106. The stiffening element 10 is shown in FIGS. 30-32 afterthe clamps 100, 102, 104, 106 are removed. As shown, a first bead 20 isflattened, and a second bead 20 is enhanced. The stiffening element 30is shown in FIGS. 41-43 after the clamps 100, 102, 104, 106 are removed.As shown, a first bead 38 is flattened, and a second bead 38 isenhanced. The stiffening element 10, 30 is ready to be utilized and maybe attached to the skin 12 by welding, tacking, bonding, fastening, orthe like.

A listing of at least a portion of the steps of a second method 1100 ofreforming or reshaping a stiffening element 10, 30 is shown in FIG. 44.The steps may be performed in the order shown in FIG. 44, or they may beperformed in a different order. Furthermore, some steps may be performedconcurrently as opposed to sequentially. In addition, some steps may beoptional or may not be performed.

At least one of two clamp assemblies is utilized in the method 1100. Afirst clamp assembly 300, as shown in FIGS. 49-52 and 56-59, includesfirst and second clamps 302A, 302B, and a resilient member 304. Eachclamp 302, as shown in FIGS. 45-48, includes an upper clamp member 306,a lower clamp member 308, and first and second fasteners 310, 312. Theupper clamp member 306 includes a top wall 314, first and second sidewalls 316, 318, first and second bolt walls 320, 322, a spring block324, a limit block 326, and a spring pin 328. The first and second sidewalls 316, 318 are spaced apart with the top wall 314 positionedtherebetween and connected to upper edges of the first and second sidewalls 316, 318. The first and second bolt walls 320, 322 are connectedto lower edges of the first and second side walls 316, 318. The springblock 324 is connected to an upper surface of the top wall 314. Thelimit block 326 is connected to a side surface of the spring block 324,and the spring pin 328 is connected to an upper surface of the springblock 324.

The lower clamp member 308 includes a central block 330 and first andsecond bolt walls 332, 334 attached to opposing lower edges of thecentral block 330. The first and second fasteners 310, 312 each includea bolt, a nut, and a spring and are similar in structure to thefasteners 112, 114. When utilized for reforming or reshaping thestiffening element 10, the first and second side walls 316, 318 and sidesurfaces of the central block 330 are angled or slanted to match theshape of the first and second shear members 16A, 16B, as shown in FIG.45. When utilized for reforming or reshaping the stiffening element 30,the first and second side walls 316, 318 and side surfaces of thecentral block 330 are orthogonal to match the shape of the first andsecond shear members 34A, 34B, as shown in FIGS. 46-48.

The resilient member 304 typically includes a spring which is utilizedin compression or in tension, although other mechanisms that provide atension force or a compression force may be utilized.

A second clamp assembly 350, shown in FIGS. 53-55, 60, and 61 and whichhas a variation in structure compared to the first clamp assembly 300and may be used as an alternative to the first clamp assembly 300,includes first and second clamps 352A, 352B, and a resilient member 354.Each clamp 352, as shown in FIG. 49, includes an upper clamp member 356,a lower clamp member 358, and first and second fasteners 360, 362. Theupper clamp member 356 includes a central block 364, first and secondbolt walls 366, 368, a spring block 370, a limit block 372, and a springpin 374. The first and second bolt walls 366, 368 are connected toopposing upper edges of the central block 364. The spring block 370 isconnected to a upper surface of the central block 364. The limit block372 is connected to a side surface of the spring block 370, and thespring pin 374 is connected to a upper surface of the spring block 370.The lower clamp member 358 includes a bottom wall 376, first and secondside walls 378, 380, and first and second bolt walls 382, 384. The firstand second side walls 378, 380 are spaced apart with the bottom wall 376positioned therebetween and connected to lower edges of the first andsecond side walls 378, 380. The first and second bolt walls 382, 384 areconnected to upper edges of the first and second side walls 378, 380.The first and second fasteners 360, 362 each include a bolt, a nut, anda spring. The resilient member 354 is substantially identical to theresilient member 304.

Either clamp assembly 300, 350 can be used in the following steps of themethod 1100.

Referring to steps 1101, 1102 and 1103, one of the two clamp assemblies300, 350 is attached to the stiffening element 10, 30. The first clamp302A, 352A is attached to the stiffening element 10, 30 to one side ofthe bead 20, 38 to be reshaped. The first clamp 302A, 352A is orientedsuch that the limit block 326 extends toward the bead 20, 38. The secondclamp 302B, 352B is attached to the stiffening element 10, 30 to theopposite side of the bead 20, 38 to be reshaped. The second clamp 302B,352B is oriented such that the limit block 326, 372 extends toward thebead 20, 38. Generally, the first clamp 302A, 352A and the second clamp302B, 352B are positioned so that the bead 20, 38 is roughly midwaybetween the two clamps 302A, 302B or 352A, 352B. Once the first clamp302A, 352A and the second clamp 302B, 352B are attached to thestiffening element 10, 30, then the resilient member 304, 354 is coupledto the spring pins 328, 374.

The first clamp assembly 300 is utilized with the stiffening element 10in FIGS. 50-52. If the resilient member 304, 354 is under tension, thenthe bead 20, 38 is to be flattened, as shown. If the resilient member304, 354 is under compression, then the bead 20, 38 is to be enhanced(not shown).

The second clamp assembly 350 is utilized with the stiffening element 10in FIGS. 53-55. If the resilient member 304, 354 is under tension, thenthe bead 20, 38 is to be enhanced, as shown. If the resilient member304, 354 is under compression, then the bead 20, 38 is to be flattened(not shown).

The first clamp assembly 300 is utilized with the stiffening element 30in FIGS. 56-59. If the resilient member 304, 354 is under tension, thenthe bead 20, 38 is to be enhanced, as shown. If the resilient member304, 354 is under compression, then the bead 20, 38 is to be flattened(not shown).

The second clamp assembly 350 is utilized with the stiffening element 30in FIGS. 60 and 61. If the resilient member 304, 354 is under tension,then the bead 20, 38 is to be flattened, as shown. If the resilientmember 304, 354 is under compression, then the bead 20, 38 is to beenhanced (not shown).

Referring to step 1104, the stiffening element 10, 30 is heated to atemperature above the glass transition temperature for the material ofthe stiffening element 10, 30. At this temperature, the stiffeningelement 10, 30 becomes malleable and the forces or pressures applied bythe resilient member 304, 354 reshape the bead 20, 38. If the resilientmember 304, 354 was in tension, then the spring blocks 324, 370 arepulled together until the limit blocks 326, 372 contact one another,which halts reshaping of the bead 20, 38. If the resilient member 304,354 was in compression, then the spring blocks 324, 370 are pushed apartfrom one another until the resilient member 304, 354 relaxes (neither incompression nor tension), which halts reshaping of the bead 20, 38. Theamount of reshaping of the bead 20, 38 may vary according to, or bedetermined by, the size of the limit blocks 326, 372 or the amount ofcompression of the resilient member 304, 354. Generally, larger-sizedlimit blocks 326, 372 result in smaller or lesser reshaping, whilesmaller-sized limit blocks 326, 372 result in larger or greaterreshaping. Also, lesser compression of the resilient member 304, 354results in smaller or lesser reshaping, while greater compression of theresilient member 304, 354 results in larger or greater reshaping.

Referring to step 1105, after a time period, the heat is reduced orremoved and the stiffening element 10, 30 is removed from the firstclamp 302A, 352A and the second clamp 302B, 352B. The stiffening element10, 30 is ready to be utilized and the attachment member 18A, 18B, 32may be attached to the skin 12 by welding, tacking, bonding, fastening,or the like.

A listing of at least a portion of the steps of a method 1200 ofattaching a stiffening element 10, 30 to a skin 12 of an aircraftcomponent is shown in FIG. 62. The steps may be performed in the ordershown in FIG. 62, or they may be performed in a different order.Furthermore, some steps may be performed concurrently as opposed tosequentially. In addition, some steps may be optional or may not beperformed.

Referring to step 1201, a skin 12 is placed against, or in contact with,an upper surface of a tool 400, as shown in FIG. 63. The upper surfaceof the tool 400 is shaped like the outer mold line of an aircraftfuselage or other component that includes the skin 12. The skin 12 isplaced such that its outer surface contacts the upper surface of thetool 400.

Referring to step 1202, the stiffening element 10, 30 is placed over theskin 12, as shown in FIG. 63. The stiffening element 10, 30 is placed sothat the attachment member 18A, 18B, 32 is in contact with the innersurface of the skin 12.

Referring to step 1203, a (surface normal) force is applied to thestiffening element 10, 30, as shown in FIG. 64. The force results in thestiffening element 10, 30, and specifically the attachment member 18A,18B, 32, being pressed against the skin 12 which is, itself, pressedagainst the tool 400. The force may be applied by human hand, a mass ofsufficient weight, a weld head on a robotic arm, or the like. The forcecauses one or more beads 20, 38 to flatten or enhance according to theshape of the tool 400. For example, if the tool 400 has a concave shape,then the force will flatten one or more beads 20, 38, as shown in FIGS.65 and 66, wherein beads 20 of the stiffening element 10 are flattened.If the tool 400 has a convex shape, then the force will enhance one ormore beads 20, 38. Typically, if the tool 400 has a convex shape, theneither multiple forces, each in a different location, are applied to thestiffening element 10, 30 or the force is applied over a greater area ofthe stiffening element 10, 30.

Referring to step 1204, the attachment member 18A, 18B, 32 of thestiffening element 10, 30 is attached to the skin 12. The attachment mayoccur by welding, tacking, bonding, fastening, or the like.

A listing of at least a portion of the steps of another method 1300 ofattaching a stiffening element 10, 30 to a skin 12 of an aircraftcomponent is shown in FIG. 67. The steps may be performed in the ordershown in FIG. 67, or they may be performed in a different order.Furthermore, some steps may be performed concurrently as opposed tosequentially. In addition, some steps may be optional or may not beperformed.

Referring to step 1301, a skin 12 is placed against, or in contact with,an upper surface of a tool 400, as shown in FIG. 68. The upper surfaceof the tool 400 is shaped like the outer mold line of an aircraftfuselage or other component that includes the skin 12. The skin 12 isplaced such that its outer surface contacts the upper surface of thetool 400.

Referring to step 1302, the stiffening element 10, 30 is placed over theskin 12, as shown in FIG. 68. The stiffening element 10, 30 is placed sothat the attachment member 18A, 18B, 32 is in contact with the innersurface of the skin 12.

Referring to step 1303, a vacuum bag 402 is placed over the stiffeningelement 10, 30 and the skin 12, as shown in FIG. 68. The vacuum bag 402is sized to cover the stiffening element 10, 30 and the skin 12 tocontact the upper surface of the tool 400.

Referring to step 1304, the vacuum bag 402 is sealed against the uppersurface of the tool 400, as shown in FIG. 69. Adhesives or otheraffixers may be used to form the seal.

Referring to step 1305, a vacuum is applied between the vacuum bag 402and the tool 400, as shown in FIG. 69. The vacuum pulls the stiffeningelement 10, 30 against the skin 12 and the skin against the tool 400, asshown in FIG. 70. The force from the vacuum bag 402 causes one or morebeads 20, 38 to flatten or enhance according to the shape of the tool400. For example, if the tool 400 has a concave shape, then the forcewill flatten one or more beads 20, 38, as shown in FIG. 70, whereinbeads 20 of the stiffening element 10 are flattened. If the tool 400 hasa convex shape, then the force will enhance one or more beads 20, 38.

Referring to step 1306, the attachment member 18A, 18B, 32 of thestiffening element 10, 30 is attached to the skin 12. The attachment mayoccur by welding, tacking, bonding, fastening, or the like.

Additional Considerations

Throughout this specification, references to “one embodiment”, “anembodiment”, or “embodiments” mean that the feature or features beingreferred to are included in at least one embodiment of the technology.Separate references to “one embodiment”, “an embodiment”, or“embodiments” in this description do not necessarily refer to the sameembodiment and are also not mutually exclusive unless so stated and/orexcept as will be readily apparent to those skilled in the art from thedescription. For example, a feature, structure, act, etc. described inone embodiment may also be included in other embodiments, but is notnecessarily included. Thus, the current invention can include a varietyof combinations and/or integrations of the embodiments described herein.

Although the present application sets forth a detailed description ofnumerous different embodiments, it should be understood that the legalscope of the description is defined by the words of the claims set forthat the end of this patent and equivalents. The detailed description isto be construed as exemplary only and does not describe every possibleembodiment since describing every possible embodiment would beimpractical. Numerous alternative embodiments may be implemented, usingeither current technology or technology developed after the filing dateof this patent, which would still fall within the scope of the claims.

Throughout this specification, plural instances may implementcomponents, operations, or structures described as a single instance.Although individual operations of one or more methods are illustratedand described as separate operations, one or more of the individualoperations may be performed concurrently, and nothing requires that theoperations be performed in the order illustrated. Structures andfunctionality presented as separate components in example configurationsmay be implemented as a combined structure or component. Similarly,structures and functionality presented as a single component may beimplemented as separate components. These and other variations,modifications, additions, and improvements fall within the scope of thesubject matter herein.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

The patent claims at the end of this patent application are not intendedto be construed under 35 U.S.C. § 112(f) unless traditionalmeans-plus-function language is expressly recited, such as “means for”or “step for” language being explicitly recited in the claim(s).

Although the technology has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the technology as recited in the claims.

Having thus described various embodiments of the technology, what isclaimed as new and desired to be protected by Letters Patent includesthe following:
 1. A stiffening element to be attached to a skin ofaircraft components for providing structural reinforcement, thestiffening element comprising: a tension and compression memberpositioned spaced apart from the skin and configured to bear tension orcompression forces that stiffen the skin and prevent the skin frombuckling or bending; a shear member connected to the tension andcompression member and configured to bear shear forces between the skinand the tension and compression member; an attachment member connectedto the shear member and configured to connect to the skin; and aplurality of beads, each bead creating an out-of-plane feature that ispositioned in at least one of the shear member and the attachmentmember, at least one of the plurality of beads configured to be reshapedto adjust a longitudinal curvature of the stiffening element.
 2. Thestiffening element of claim 1, wherein the shear member includes a firstshear member connected to a first edge of the attachment member and asecond shear member connected to a second edge of the attachment member,and the tension and compression member includes a first tension andcompression member connected to the first shear member and a secondtension and compression member connected to the second shear member. 3.The stiffening element of claim 2, wherein each bead starts near an edgeof the first shear member adjacent to the first tension and compressionmember, extends in a transverse direction across the first shear member,extends into and across the entire width of the attachment member,extends in a transverse direction across the second shear member, andends near an edge of the second shear member adjacent to the secondtension and compression member.
 4. The stiffening element of claim 1,wherein the shear member includes a first shear member connected to afirst edge of the tension and compression member and a second shearmember connected to a second edge of the tension and compression member,and the attachment member includes a first attachment member connectedto the first shear member and a second attachment member connected tothe second shear member.
 5. The stiffening element of claim 4, whereinthe plurality of beads includes a plurality of beads formed in each ofthe first and second attachment members.
 6. The stiffening element ofclaim 1, wherein each bead has an arch or roughly paraboliccross-sectional shape.
 7. The stiffening element of claim 1, whereineach bead is configured to be reshaped in a first manner to adjust thelongitudinal curvature of the stiffening element in a first directionand reshaped in a second manner to adjust the longitudinal curvature ofthe stiffening element in a second direction, opposite to the firstdirection.